As disclosed in U.S. Pat. No. 8,549,316, by the inventor hereof, and incorporated by reference herein, a hand plane is very important to woodworkers and furniture makers because it may be one of the best tools for creating a finished flat surface on wood. Superior results may be achieved with the hand plane because the wood fibers are cleanly severed, not tom, which creates a smooth, continuous surface ready for finishing. This is true even where the surface comprises two or more separate boards that have been joined side-by-side to create a larger piece.
In fine woodworking, the cutting blade of a hand plane preferably includes a crown on a cutting edge to impart the final surface finish. Such crowned cutting blades cut a shaving from a wide board of wood, leaving no noticeable ridges in the wood because the shaving produced will be thickest along a longitudinal center line and gradually taper in thickness to nothing in the lateral directions, left and right of the center line of the shaving. The crowned cutting edge of the cutting blade of the hand plane prevents any trails in the wood which are detectable by feel or appearance. A wood surface properly planed with a crowned cutting blade will be continuous and smooth and will reveal the grain and color of the wood.
Sharpening a cutting blade of a hand plane iron to create a crown in the cutting edge of the blade that prevents trails in wood surfacing, finishing, and smoothing is a difficult procedure.
One improved method for creating a crown in the cutting blade of a hand plane disclosed in the '316 patent discussed above relies on providing a diamond-coated sharpening plate having a concave surface of a large radius, e.g., in the range of about 150 inches to about 600 inches that is located along the width of sharpening plate. A crown in the cutting edge of the hand plane iron is formed when the bevel of the hand plane iron is stroked fore-and-aft longitudinally against the sharpening surface of the sharpening plate with the cutting edge approximately perpendicular to the cylindrical axis of the cylindrical curvature.
Over the history of hand tools in woodworking, especially those tools with cutting blades or knife edges, sharpening has been done by scratching away fine particles of metal from the intersecting faces which form the edge. These scratches were typically created by abrasive grit in natural stones. Refinements to abrasive grit in natural stones included harder steel edge and harder grit in a series of progressively finer particles. In recent times, man-made diamond is often utilized in manual sharpening of cutting blades because diamond is the hardest and most durable of abrasive grits. Diamond-coated sharpening plates typically include a steel plate that has a top surface having the large radius as disclosed in the '316 that is electroplated diamond. The diamond-coated sharpening plates may have various grit sizes, e.g., 60μ, 45μ, 25μ, and 91μ. Polishing cutting blades is typically done with water stones and leather strops.
Chisels are less of a challenge to sharpen because their edges are straight. As discussed above, the cutting blade of a hand plane will leave trails in smoothing broad wood surfaces if the cutting edge of the cutting blade is straight. Slightly curving the cutting edge of cutting blade to create a crown, often referred to as crowning, that prevents trails is challenging.
One conventional method of crowning typically practiced by full time professional woodworkers relies on off-hand grinding a flat bevel of a cutting blade at about 25° on a grind wheel followed by off-hand curving during honing and polishing on flat grit surfaces with lateral force shifts. This force shifting requires significant skill and the crowns created in the cutting blade may be inconsistent.
In current times, hobbyist woodworkers outnumber professional woodworkers. Thus, the need for improved sharpening techniques to create a crown in the cutting edge of a cutting blade that require less skill, less expense, and less time is paramount. The hobbyist woodworker typically prefers spending less time sharpening and more time working the wood.
With durable-coated sharpening plates discussed above and the need for improved sharpening techniques to create a crown in the cutting edge of a cutting blade that requires less skill and time, the curved diamond-coated sharpening plates as disclosed in '316 patent attracted market interest. However, the large-sized, curved, diamond-coated sharpening plates as disclosed in the '316 patent, added costs. In response, smaller, narrow-width diamond-coated sharpening plates where developed such that the curve having a large radius is located along the length of diamond-coated sharpening plate. The new design enabled side-stroking and reduced the width of the sharpening plate by half; which reduced the cost by half. Side-stroking proved difficult for many hobbyist woodworkers relying on off-hand methods without any type of sharpening jig.
A sharpening jig may be used to create a crown on the cutting edge of a cutting blade to overcome the problems discussed above. One conventional sharpening jig is disclosed in U.S. Pat. No. 9,221,144, by the inventor hereof, incorporated by reference. As disclosed in the '144 patent, the sharpening jig for a cutting blade includes a baseplate, a protractor plate, an incline plate for securing a cutting blade and defining a sharpening angle, a push plate to position user applied force and reduce do-stabilizing moments. The sharpening jig also includes one or more glides, riding the bench top rather than the grit surface, located pt the back of the sharpening jig, configured to longitudinally and/or laterally level the baseplate with respect to a level abrasive surface of the sharpening base to allow movement of the jig by a user to create a crown in the cutting edge of the cutting blade.
In one example, to sharpen a cutting blade and create a crown on the cutting edge of the cutting blade with the sharpening jig as taught by '144 patent, or similar type sharpening jig, a large-sized diamond-coated sharpening plate or stone having concave surface with a large radius, e.g., in the range of about 150 inches to about 600 inches, is placed proximate the front of the sharpening jig. The one or more glides at the back of the jig as disclosed in the '144 patent longitudinally and/or laterally level the base plate of the sharpening jig with respect to the level abrasive surface of the large-sized diamond-coated sharpening plate to allow stroking in all horizontal orientations by a user. The sharpening jig is moved fore-and-aft in a longitudinal direction over the large-sized concave shaped diamond-coated sharpening plate or stone to create the crown on the cutting edge of the cutting blade. In one example, the large-sized diamond-coated sharpening plate or stone is approximately 10 inches in length and has a width of a width of about 4 inches, or similar large-size known to those skilled in the art. However, the large-sized diamond-coated sharpening plate or stone is very expensive.
To reduce the cost associated with large-sized sharpening plates or stones, a series of smaller, narrow-width diamond-coated sharpening plates having progressively smaller grit sizes each having concave surface with a similar large radius may be utilized with the sharpening jig as disclosed in the '144 patent, or similar type sharpening jig. In one example, each of the smaller diamond-coated sharpening plates are approximately 8 inches in length and have a width of about 1½ inches.
In operation, the sharpening jig with the cutting blade are side-stroked on the curved surface of the smaller-sized diamond-coated plate to sharpen the cutting blade and create a crown in the cutting edge of the cutting blade. Similarly, the glides at the back of the jig as disclosed in the '144 patent adjust to levels the base plate of the sharpening jig with respect to the level abrasive surface of the small-sized diamond-coated sharpening plate to allow movement of the jig in all horizontal directions by a user to create the sharpened edge on the cutting blade with a crown. However, even the smaller sized diamond-coated sharpening plates are expensive.
Most hobbyists and professional woodworkers own conventional typically inexpensive flat sharpening plates and stones. Thus, there is a need for a system and method which can utilize conventional inexpensive flat sharpening plates and stones with a sharpening jig to easily and effectively create a crown on the cutting edge of the cutting blade for a hand plane without the need for expensive concave shaped diamond-coated sharpening plates or stones.